The present invention relates to room temperature vulcanizable silicone rubber compositions and more particularly the present invention relates to room temperature vulcanizable silicone rubber compositions in which there is a self-bonding additive selected from silyl maleates, silyl fumarates and silyl succinates such that the composition will bond to various substrates in the absence of a primer.
Room temperature vulcanizable silicone rubber compositions are well known in silicone chemistry. Basically these compositions break down to one-component or one-part room temperature vulcanizable silicone rubber compositions and two-component or two-part room temperature vulcanizable silicone rubber compositions. Basically, the two-component room temperature vulcanizable silicone rubber composition comprises a silanol terminated base polymer, an alkyl silicate or the partial hydrolysis product of an alkyl silicate as a crosslinking agent, a filler and a metal salt of a carboxylic acid as the curing catalyst.
Normally, the crosslinking agent is packaged or prepared separately from the silanol base polymer and when it is desired to cure the composition the two components are normally mixed and applied to whatever shape it is desired, whereupon the composition will cure either in the presence of or in the absence of moisture to a silicone elastomer. There are also SiH-olefin platinum catalyzed two-component room temperature vulcanizable silicone rubber compositions, however, these will not be discussed in detail since they form no part of the present invention.
With respect to the one-component system, or one-part room temperature vulcanizable silicone rubber compositions, such compositions generally comprise a silanol terminated diorganopolysiloxane polymer as the base polymer and acyloxy functional silane or an alkoxy functional silane or an amide functional silane or a ketoximino functional silane or various other types of functional silanes and finally a curing catalyst which in the case of the acyloxy functional silane crosslinking agent is a metal salt of a carboxylic acid, most typically a tin salt of a carboxylic acid. In the case of the alkoxy functional silane crosslinking agents the catalyst is frequently a titanimum compound. To these three ingredients there may be added other ingredients such as fillers, flame-retardant additives, etc. These ingredients in the one-part of one-component room temperature vulcanizable silicone rubber compositions are normally mixed together in the anhydrous state and packaged as such in waterproof containers. When it is desired to cure the composition, the one-component room temperature vulcanizable silicone rubber composition is taken out of the waterproof container, applied to whatever form it is desired and exposed to atmospheric moisture. In the presence of atmospheric moisture, such compositions cure to a silicone elastomer. Thus, it can be seen that the one-component systems have the advantage over the two-component systems in that the components are already mixed and an unskilled worker in the field does not have to take measured amounts of the two-components and mix them together so as to produce the desired curable composition as is the case in the two-component system. However, both of these compositons have found their place in the field. Examples of such room temperature vulcanizable silicone rubber compositions are for instance to be found in U.S. Pat. No. 3,065,194, Bruner U.S. Pat. No. 3,035,016, in Ceyzeriat U.S. Pat. No. 3,133,891, in Brown et al. U.S. Pat. No. 3,161,614, in Cooper U.S. Pat. 3,383,355, in Matherly U.S. Pat. No. 3,499,859, in Cooper et al. U.S. No. 3,542,901, in Brown et al. U.S. Pat. No. 3,122,522, in Brown et al. U.S. Pat. No. 3,170,894, in Weyenberg U.S. Pat. No. 3,175,993, in Smith and Hamilton U.S. Pat. No. 3,689,454, and U.S. Pat. No. 3,779,986, in Weyenberg U.S. Pat. No. 294,739 and 3,334,067 and Clark et al. U.S. Pat. No. 3,719,635. Also, special notice should be taken of Beers U.S. Pat. No. 3,382,205 which discloses a polysiloxane additive for one-component room temperature vulcanizable silicone rubber compositions.
All these patents relate to the basic room temperature vulcanizable silicone rubber compositions or improvements thereover. One particular concern, with respect to room temperature vulcanizable silicone rubber compositions, was the adhesion of such compositions to various substrates, such as for instance metallic substrates, plastic substrates, cellulosic substrates, masonry substrates and so forth. Early in the development of such compositions primers were utilized to enhance adhesion, whereupon the primer was applied over the surface to which the silicone composition was to be applied to and then the silicone composition would be applied thereover and cured at room temperature to form a silicone elastomer, which would bind or adhere to the substrate because of the presence of the primer. Although this was advantageous, nevertheless, in the application of the composition, it required the use of an extra step. Since labor is expensive it became desirable to eliminate such primer application step in the use of room temperture vulcanizable silicone rubber compositions. Accordingly, various additives were devised to be added to room temperature vulcanizable silicone rubber compositions prior to their being packaged in containers such that the compositions when applied to a substrate would cure to a silicone elastomer, which would adhere to the substrate in the absence of a primer. An example of such an additive, which shall be referred to as a self-bonding additive in two-part room temperature vulcanizable silicone rubber compositions, is for instance to be found in Bessmer or Lampe U.S. Pat. No. 3,888,815, which discloses the use of nitrogen functional silanes are self-bonding additives for two-component room temperature vulcanizable silicone rubber compositions. However, such nitrogen functional silanes while being helpful self-bonding additives for two-component room temperature vulcanizable silicone rubber compositions were not very effective for one-component RTV (Room Temperature Vulcanizable) silicone composition.
Prior to these developments in two-component RTV self-bonding additives were developed for various one-componnt RTV compositions having various types of crosslinking agents. For instance, for the acetoxy functional one-component RTV system there was developed a diacyloxy, dialkoxy silane as a self-bonding additive which was very effective. Such an additive is disclosed, for instance, in Kulpa U.S. Pat. No. 3,296,161. Such a self-bonding additive was found to be very effective for a system in which the crosslinking agent was methyltriacetoxysilane. Another example of a self-bonding additive is that to be found in Beers U.S. Pat. No. 4,100,129, which discloses the use of a silylisocyanurate as a self-bonding additive for a one-part RTV system in which the crosslinking agent was methyltrimethoxysilane and the curing catalyst was a titanium chelate catalyst. However, there is always a desire to find further self-bonding additives that can be added to one component RTV systems, which are as good as the silyl isocyanurates or even better.
Heat vulclanizable silicone rubber compositions are also well-known. Such compositions generally comprise of vinyl-containing polysiloxane gum and of a viscosity varying from one million to three hundred million centipoise at 25.degree. C., silica filler, various process aids and a peroxice curing catalyst. When the composition is heated at elevated temperatures and preferably above 100.degree. C., the composition dures to a silicone elastomer. The presence of moisture has nothing to do with the cure of such compositions, but the cure is carried out by free radicals released by the peroxide when it is heated at elevated temperatures. For such compositions see Selin and Berger U.S. Pat. No. 3,780,080, in which silyl maleates and silyl fumerates and also maleate functional polysiloxanes and fumerate functional polysiloxanes are used as self-bonding additives. This patent is one of a number of divisional patents which was selected at random to illustrate the use of such maleates and fumerates as self-bonding additives for heat vulcanizable silicone rubber compositions.
Also note should be taken of Berger and Selin U.S. Pat. No. 3,759,968, which discloses the preparation and presence of silyl maleates and silyl fumerates as a compounds. Recently, there has been developed a one component RTV system which utilizes as a crosslinking agent, an organosilane, having as functional groups carboxyl radicals of from 6 to 10 carbon atoms. The known self-bonding additives for one-part RTV systems functions somewhat with such a one-part RTV composition. However, they were not found to be as effective as would be desired. Such a one-component RTV system and specifically one having as the crosslinking agent methyl tris 2-(ethylhexanoxy) silane with various self-bonding additives is disclosed for instance in the patent application of M. D. Beers, Ser. No. 919,544, filed on June 27, 1978. It should be noted herein that all the foregoing patents and patent applications mentioned in this specification are incorporated by reference under the present specification.
Accordingly, it became desirable to develop a new self-bonding additive for a one-component RTV system which utilizes a carboxyl functional silane as a crosslinking agent, as for instance disclosed in the Beers Pat. applications of Ser. No. 919,544. Accordingly, it was highly unexpected that silyl maleates and fumerates of the foregoing heat vulcanizable silicone rubber compositions could be utilized as self-bonding additives for one-component RTV systems.
It is one object of the present invention to provide for a self-bonding one-part RTV composition which utilizes as its self-bonding additives silyl maleates, silyl fumerates and silyl succinates.
It is an additional object of the present invention to provide for self-bonding one-part RTV system which has as the crosslingking agent carboxyl functional silane where the carboxyl group contains 6 or more carbon atoms in which the self-bonding additive is a silyl fumerate, silyl maleate or silyl succinates or mixtures thereof.
It is a further object of the present invention to provide for self-bonding one-part RTV compositions which will adhere to various plastic, metal, cellulosic and masonry substrates in the absence of a primer where the self-bonding additive is a silyl maleate, silyl fumerate or silyl succinate.
There is still an additional object of the present invention to provide for a laminate which is formed from a substrate selected from metals, plastics, cellulosic substrates and masonry substrates, to which there is applied a self-bonding one-part RTV composition which adheres to the substrate in the absence of a primer and in which system the cross-linking agent is selected from hydrocarbonoxy functional silanes and carboxyl functional silanes.
It is yet an additional object of the present invention to provide for a process for producing a self-bonding one-component RTV system, which has as the crosslinking agent a hydrocarbonoxy functional silane or a carboxyl functional silane in which the self-bonding additive is selected from silyl maleates, silyl fumerates and silyl succinates. These and other objects of the present invention are accomplished by means of the disclosure set forth herein below.